I. Field of the Invention
The present invention pertains to drivers for radiating elements and electronically steerable arrays.
More particularly the present invention pertains to a communication device having a Transmit/Receive (T/R) element fabricated from HEMT (High Electron Mobility Transistor) technology, that advantageously drives multiple radiating elements.
II. Discussion of the Background
Historically, electronically steerable phased arrays have utilized two types of designs.
With reference to FIG. 1, the passive Electronically Steerable Array (ESA) 14 has a transmitter/receiver 18 for driving a plurality of arrayed phase shifters 16 that are connected to a radiating element or elements 10. The array 14 is passive in that it is dependent upon a single high-peak-power tube transmitter/receiver 18. Should the transmitter receiver 18 fail, the entire array 14 becomes inoperational.
In FIG. 2, an active Electronically Steerable Array 20 has many transmit receive elements as demonstrated in a row 22 of transmit/receive elements. Each of the transmit/receive elements of row or network 22 is directly connected to a corresponding phase element in row or network 24 of phase elements. In the active ESA of FIG. 2, the row 22 of T/R elements is positioned between the radiating element or elements 26 and the row of phase elements 24. In FIG. 4, the schematic diagram of an array column 25 demonstrates the element geometry of an active ESA in that the transmit/receive element 221 is positioned between the phase element 241 and the radiating element 261.
The schematic diagram of FIG. 3 will provide explanation for the reason transmit/receive element 221 of the active ESA is positioned between the phase element 241 and the radiating element 261.
With reference to FIG. 3, transmit/receive element 221 is comprised of a number of electrical components. A switch 48 alternatively connects radiating element 261 to low noise amplifier 28 during receive mode or to power amplifier 46 during transmit mode. Low-noise amplifier 28 connects to band-pass filter 30 that connects to a mixer 32. Mixer 32 mixes the received signal with a current received from an oscillator with the mixed signal proceeding to amplifier 34. Amplifier 34 connects to a switch 36 which opens and closes depending upon the mode of operation. Amplifier 38 is located between and connects to phase shifter 241 and to multiplier or mixer 42. A mixed signal proceeds from mixer 42 to band-pass filter 44 to power amplifier 46. When switch 48 connects to power amplifier 48, a signal can be transmitted through radiating element 261.
To achieve the best performance for active ESA array elements such as those depicted in FIGS. 2-4, the low noise amplifier 28 needs to be positioned as close as possible to the radiating element 261 due to the relatively low peak power of the transmitter/receiver 221. As the distance of the low noise amplifier 28 from the radiating element increases, signal loss increases and performance decreases.
The transmitter/receiver 18 of the passive ESA of FIG. 1 has sufficient power to drive the radiating elements 10, but since the large drive signal has to travel through the phase shifters 16, unwanted noise is created. Further, as has been pointed out, should the transmitter/receiver 18 fail, the entire device will fail.